Nonwoven fabric, and process for producing the same

ABSTRACT

In a fibrous web, press-welded line portions are formed, and press-welded dot portions are formed in portions other than the press-welded line portions. The formation of the press-welded line portions makes it possible to raise the surface of the fibrous web, to increase the bulkiness of the nonwoven fabric and to make the nonwoven fabric soft. Further, figures are drawn by the press-welded line portions, whereby the nonwoven fabric comes to have an excellent appearance in comparison to a conventional nonwoven fabric.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a nonwoven fabric which is usedin a disposable diaper, a sanitary napkin or kitchen utensils. Morespecifically, the present invention relates to a nonwoven fabric whichhas a solid, soft appearance, looks solid and soft and which canmaintain a satisfactory bond strength of fibers, as well as to a processfor producing the same.

[0003] 2. Prior Art

[0004] There is a nonwoven fabric having a base weight of at least 15g/m² and at most 45 g/m² which fabric is embossed to have a raised linepattern (embossed pattern). In this nonwoven fabric, fibers on thesurface of the fibrous web formed of fluffed fibers are adheredrelatively densely by a predetermined method, for example, byheat-welding or entangling, and the adhered portions are recessed. Theembossed pattern has been provided through this adhesion.

[0005] Since, however, the embossed pattern is formed densely throughoutthis nonwoven fabric, the difference in height between the recessedportion given through this embossing and the other portion in thenonwoven fabric is small. Accordingly, the surface of the nonwovenfabric is less raised, that is, it has a less solid appearance.Consequently, it does not look soft, nor does it feel soft when onetouches it.

[0006] Meanwhile, as shown in FIG. 9, in a product in which welded dotportions M are formed in a fibrous web W at a fixed pitch, a specificvolume (volume/weight) is relatively large in the portions other thanthe welded portions M, and it can easily be given a solid appearance.

[0007] Nevertheless, in the product shown in FIG. 9, the area of thewelded portion M is small, the outer periphery of each welded portion Mis short, and the nonwoven fabric is less raised. Therefore, thedifference in volume between the welded portion M and the surroundingportion is small, so that the raising of the nonwoven fabric isunsatisfactory. Thus, the pattern is monotonous, lacking variety when itis adhered to, for example, an outer surface of an outer film in adisposable diaper.

[0008] Further, a nonwoven fabric shown in FIG. 9 is laminated on theouter surface of the outer film in a disposable diaper or the like, anda resin film of the outer film and the nonwoven fabric are welded; thiswelded portion has a pattern or a figure. However, in case the nonwovenfabric having welded dot portions M as shown in FIG. 9 is further weldedto the resin film, the portions welded to the resin film are overlappedwith the welded dot portions M, and the area of the welded portions islarger than the area of the nonwoven fabric. Thus, the line patternformed by the welded portions M lacks sharpness, and the nonwoven fabricdoes not look solid. Further, as the resin film and the nonwoven fabricare welded to each other in the welded portions M, these portions feelstiff. Further, when an air-permeable film is used as the resin film andpatterned or figured welded portions are formed in the resin film andthe nonwoven fabric, the air permeability of the resin film is reducedas a whole.

[0009] Besides, the conventional nonwoven fabric is formed of anuncolored fibrous web in many cases. Even if it is formed of a coloredweb, the overall nonwoven fabric has a single color. For this reason,there is not a product which has a color contrast and in which a patternis expressed upon using a bulkiness of the nonwoven fabric.

SUMMARY OF THE INVENTION

[0010] The present invention aims to solve the abovementioned problemsassociated with the prior art. It is an object of the present inventionto provide a nonwoven fabric which makes vivid a line pattern formedwith press-welded portions by improving the shape of the press-weldedportions, which can be rendered bulky by raising the non-press-weldedportions, which looks soft and feels soft when touched with the hand, aswell as a process for producing the same.

[0011] Another object of the present invention is to provide a nonwovenfabric which can have a pattern or a figure by improving the shape ofthe press-welded portions, for example, which can have a pattern or afigure in the outer surface when used as an outer sheet of a disposablediaper for babies or little children, which can increase a beautifulappearance and in which the presence or absence of urine in a diaper canvisually be observed in the press-welded portions from outside thediaper, as well as a process for producing the same.

[0012] Still another object of the present invention is to provide anonwoven fabric in which the shape of the press-welded portions isimproved to make bulky the non-press-welded portions and thepress-welded portions can provide a clearer pattern to give a colorcontrast, as well as a process for producing the same.

[0013] The present invention is to provide a nonwoven fabric havingpartially press-welded portions that are recessed in the surface of afibrous web, characterized in that the press-welded portions have acontinuous line or uncontinuous line (broken line) pattern with a curvedor square part, and the portions other than the continuous line oruncontinuous line press-welded portions in the fibrous web have a raisedpattern relative to the recess of the press-welded portions.

[0014] As the fibrous web which is a material of this nonwoven fabric,the web formed of relatively dense fibers having a base weight of atleast 15 g/m² and at most 45 g/m² is preferably used. When the specificvolume of the press-welded portions is at least 3 cm³/g and at most 10cm³/g and the specific volume of the non-press-welded portions is atleast 10 cm³/g and at most 30 cm³/g, the non-press-welded portions inthe fibrous web become bulky, and the boundary between the press-weldedportions and the non-press-welded portions make clear and the nonwovenfabric comes to look solid.

[0015] The portion surrounded with the continuous line or uncontinuousline press-welded portions is formed in the above-mentioned non-wovenfabric, and the fibrous web in the surrounded portion is preferablyraised relative to the recessed press-welded portions.

[0016] It is further preferable to form a plurality of press-welded dotportions other than the continuous line or uncontinuous linepress-welded portions. In this case, it is advisable that thepress-welded dot portions are formed where these portions do not overlapwith the continuous line or uncontinuous line press-welded portions ofthe fibrous web. The continuous line or uncontinuous line press-weldedportions are preferably spaced apart from the adjacent press-welded dotportions by at least 1 mm, preferably at least 1 mm and at most 5 mm.

[0017] It is still further preferable that the total area of thepress-welded dot portions in the nonwoven fabric is the same as, or lessthan, the total area of the continuous line or uncontinuous linepress-welded portions.

[0018] It is furthermore preferable to use fibers having a square oruneven cross-section as a starting material of the fibrous web.

[0019] It is moreover preferable that a color sheet is overlaid on thereverse surface of the nonwoven fabric and they are adhered so that thecolor of the color sheet is seen through the press-welded portions ofthe nonwoven fabric. This procedure gives the sharp color contrastbetween the recessed press-welded portions of the fibrous web and thebulky portions of the fibrous web and makes clear the pattern drawn bythe press-welded portions.

[0020] A process for producing a nonwoven fabric in the presentinvention comprises a step of forming a fibrous web from startingfibers, a step of feeding the fibrous web between a hot roller providedon the surface with curved or square line or uncontinuous line projectedportions and a hot roller having a smooth surface, and a step of holdingthe fibrous web between the hot rollers provided on the surface with theprojected portions and the hot roller having the smooth surface, andpress-welding the fibers of the fibrous web with the projected portionson the surface of the hot roller to partially recess the fibrous web andform the press-welded portions.

[0021] A plurality of dot-shaped projected portions, in addition to theabove-mentioned continuous or uncontinuous line projected portions areformed on the surface of the hot roller.

[0022] In a method of placing the color sheet under the nonwoven fabricand welding them, a colorless fibrous web is laminated on a dyed orcolored thermoplastic sheet, the laminate is fed between the two hotrollers and held therebetween, and the thermoplastic sheet and thefibrous web are press-welded together with the projected portions formedon the surface of the hot roller to give press-welded portions.

[0023] In another method, a fibrous web formed of colorless fibers islaminated on a color fibrous web formed of dyed or colored fibers, thelaminate of these fibrous webs is fed between the two hot rollers andheld therebetween, and the color fibrous web and the colorless fibrousweb are partially press-welded with the projected portions formed on thesurface of the hot roller to give press-welded portions.

[0024] In this nonwoven fabric, the fibrous web is formed ofthermoplastic short fibers having a fiber length of at least 30 mm andat most 70 mm, and fed to the hot rollers. When the fibrous web ispassed through the hot rollers, it is partially pressed with theprojected portions of one hot roller, and heated to give partiallypress-welded portions. In the present invention, it is assumed that thethermoplastic fibers of the fibrous web are not welded in the portionsother than the above-mentioned press-welded portions. However, since thefibrous web may be raised on the portions other than the recesses in thepress-welded portions of the fibrous web, the thermoplastic fibers ofthe fibrous web may be hot-welded in the portions other than thepress-welded portions.

[0025] The press-welded dot portions formed with the projected portionsof the hot roller refer to circular, elliptical or very short linepress-welded portions. For example, circular-, elliptical- or very shortline-shaped projected portions are formed on the surface of the hotroller at a fixed space. The press-welded dot portions refer to those inwhich the area of each of these portions is much smaller than that ofeach of the continuous line or uncontinuous line press-welded portions.The uncontinuous line press-welded portions refer to short linepress-welded portions which are spaced apart from each other.

[0026] The press-welded portions are not only those recessed in onesurface of the nonwoven fabric as shown in FIG. 8, but also thoserecessed in both surfaces of the nonwoven fabric.

[0027] The continuous line or uncontinuous line press-welded portionsare formed in the nonwoven fabric of the present invention. Thecontinuous line or uncontinuous line press-welded portions may bestraight lines, but preferably curved lines (arcked lines) or squarelines. When the continuous line or uncontinuous line press-weldedportions are the straight lines, a pattern can be formed by crossing thestraight line press-welded portions. When the press-welded portions arethe continuous lines or the uncontinuous lines, the surface of thefibrous web is raised in the boundary between the press-welded portionsand the non-press-welded portions, and the raised portions becomeconspicuous as shown in FIG. 3. Consequently, the overall nonwovenfabric becomes bulky and looks solid. It looks or feels soft compared tothe conventional nonwoven fabric. In the continuous line or uncontinuousline press-welded portions, the fibers become filmy and transparent orsemitransparent. Therefore, the color contrast between thesepress-welded portions and non-press-welded portions goes sharp. Thus,the continuous line or uncontinuous line press-welded portions lookclear; the nonwoven fabric improves in the appearance as compared to theconventional nonwoven fabric.

[0028] Fibers having a cross-section shown in FIG. 4(A), (B) or (C) maybe used as starting fibers of the fibrous web. The fibers having theabove-mentioned cross-section reflect light diffusely to increase thewhiteness of the fibrous web. Accordingly, the raised portions otherthan the press-welded portions come to have a clear white color.Meanwhile, the press-welded portions become transparent orsemitransparent. Therefore, the contrast between the transparent orsemitransparent press-welded portions and the raised white portionsother than the press-welded portions is made even clearer.

[0029] In the present invention, the continuous line or uncontinuousline press-welded portions are made to have a curved or square shape tobe able to provide a predetermined pattern. This pattern is given fromthe curved (arched) or square shape, or a combination thereof continuousline or uncontinuous line press-welded portions or a combinationthereof. This pattern is provided by a figure, a combination of figures,characters, symbols, a combination of characters and symbols, acombination of figures and characters, and a combination of figures andsymbols.

[0030] As shown in an enlarged view of FIG. 2, when the fibrous webconstituting the nonwoven fabric is partially press-welded in theproduction of the nonwoven fabric, the pattern (or the figure) isexpressed from the press-welded portions to give an appearance differentfrom that of the conventional nonwoven fabric shown in FIG. 9. Thepattern is expressed from the continuous line or uncontinuous linepress-welded portions. The surface of the fibrous web is raised from thecontinuous line or uncontinuous line press-welded portions, and thenonwoven fabric is bulky, solid and soft visually and tactually.Further, the contrast between the continuous line or uncontinuous linepress-welded portions and the non-press-welded portions becomes clear,and the pattern is seen sharply.

[0031] Moreover, when a color sheet is adhered to the reverse surface ofthe nonwoven fabric having the press-welded portions, the color of thecolor sheet on the reverse surface appears through the transparent orsemitransparent press-welded portions, and the sharp color contrast isgiven between the press-welded portions and the non-press-welded bulkyportions. Especially when using fibers having a square or unevensectional shape in the nonwoven fabric, the non-press-welded portionshave a clear white color, making sharp the contrast between the color ofthe color sheet on the press-welded portions and the white color of thenon-press-welded portions.

[0032] For example, a colored resin film is used as a color sheet. Thecolored resin film is adhered to the reverse surface of the nonwovenfabric having the press-welded portions that form the pattern. Thenonwoven fabric having the pattern and the colored resin film may beadhered partially or wholly using a hot melt adhesive or anothertransparent adhesive.

[0033] It is also possible that the non-press-welded fibrous web islaminated on the colored thermoplastic resin film, the coloredthermoplastic resin film and the fibrous web are press-welded together,and the colored resin film and the fibrous web are press-welded togetherin the press-welded portions.

[0034] When a resin sheet having a light warm color such as pink is usedas the colored resin film, the nonwoven fabric looks softer. When usinga resin sheet having a color such as light blue, a user can feel cleanand fresh.

[0035] The nonwoven fabric of the present invention may have only curvedor square continuous line or uncontinuous line (broken line) likepress-welded portions and be free from press-welded dot portions.However, it is preferable that there are the above-mentioned pluralpress-welded dot portions besides the continuous line or uncontinuousline press-welded portions.

[0036] Further, portions surrounded by the curved or/and squarecontinuous line or uncontinuous line press-welded portions are formed inthe above-mentioned pattern. It is advisable that the above-mentionedplural press-welded dot portions are formed inside and outside thesurrounded portions.

[0037] When the press-welded dot portions are formed inside and outsidethe surrounded portions other than the continuous line or uncontinuousline press-welded portions that give the pattern as mentioned above, itis possible to increase the tensile strength of the nonwoven fabric inthe portions other than the continuous line or uncontinuous linepress-welded portions, and also to prevent fluffing of the fibrous webin the portions other than the continuous line or uncontinuous linepress-welded portions.

[0038] In the present invention, when forming the continuous line oruncontinuous line press-welded portions and the press-welded dotportions, it is advisable that these portions are provided so as not tooverlap with each other. That is, as shown in FIG. 2, it is advisablethat the press-welded dot portions are formed in spaced apartrelationship with the continuous line or uncontinuous line press-weldedportions at a fixed space (for example, at least 1 mm and at most 5 mm),and that the press-welded dot portions are formed in both sides of thecontinuous line or uncontinuous line press-welded portions at the samespace. In this construction, the pattern drawn by the continuous line oruncontinuous line press-welded portions does not overlap with thepress-welded dot portions, and it tends to become clear.

[0039] It is further advisable that the total area of the press-weldeddot portions occupied in the nonwoven fabric is the same as, or lessthan, the total area of the continuous line or uncontinuous linepress-welded portions occupied in the nonwoven fabric, whereby thepattern drawn by the continuous line or uncontinuous line press-weldedportions is not erased by the press-welded dot portions, making itpossible to make clear the pattern.

BRIEF DESCRIPTION OF THE DRAWINGS

[0040]FIG. 1 is a plan of a part of a nonwoven fabric according to thepresent invention.

[0041]FIG. 2 is an enlarged plan of a part of a nonwoven fabric shown inFIG. 1.

[0042]FIG. 3 is an enlarged perspective view of a part of a nonwovenfabric shown in FIG. 2.

[0043] FIGS. 4 (A), (B) and (C) are each a cross-sectional view of astarting fiber used in the nonwoven fabric of the present invention.

[0044]FIG. 5 is a perspective view of the nonwoven fabric shown in FIG.4 under which a color sheet is placed.

[0045]FIG. 6 is a perspective view of an open-type disposable diaperformed by using the nonwoven fabric of the present invention.

[0046]FIG. 7 is a front view illustrating a step of welding a nonwovenfabric using hot rollers.

[0047]FIG. 8 is an enlarged view of a part of FIG. 7.

[0048]FIG. 9 is a perspective view showing the appearance of theconventional nonwoven fabric of this type.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0049] In a non-woven fabric S shown in FIG. 1, a fibrous web W formedof thermoplastic short fibers each having a length of from 30 mm to 70mm is partially pressed and welded to form press-welded portions.

[0050] The fibrous web W is formed of thermoplastic fibers selected frompolyethylene fibers and polypropylene fibers, or of a mixture ofpolyethylene fibers and polypropylene fibers. Or it is formed ofcomposite fibers of a polyester and polyethylene, composite fibers ofpolypropylene and polyethylene, or a mixture of both composite fibers.

[0051] The above-mentioned press-welded portions comprise continuousline press-welded portions and press-welded dot portions which areformed at a fixed space. A design (figure) is expressed by thecontinuous line press-welded portions. This design comprises acombination of 9 patterns A to P in FIG. 1, and these 9 patterns arerepeatedly formed in the flat surface of the nonwoven fabric S (fibrousweb W).

[0052]FIG. 2 is an enlarged view of the pattern E in the nonwoven fabricS shown in FIG. 1.

[0053] In FIG. 2, the hatched portions are press-welded portions inwhich fibers of the nonwoven fabric are press-welded, and no fibers arewelded in the other portions. Accordingly, the thickness of thenon-press-welded portions of the nonwoven fabric is fixed, for example,0.5 mm.

[0054] Portions indicated at Hd in FIG. 2 are press-welded dot portions,and the other welded portions are press-welded line portions. In thenonwoven fabric shown in FIG. 2, the continuous line press-weldedportions are formed longer than the press-welded dot portions Hd.

[0055] Of the press-welded line portions, H1 has a curved shape (archedshape) (a), a square shape (b) and a straight line pattern (c). Thispress-welded portion H1. expresses a contour of a “chick”. A fixedportion (i) is surrounded by this press-welded line portion H1. Thepress-welded line portion H2 expressing a “feather of a chick” and thepress-welded line portion H3 expressing an “eye of a chick” are formedin this surrounded portion (i). Both of the press-welded line portionsH2, H3 are curved.

[0056] The press-welded dot portions Hd are formed both inside andoutside the portion (i) surrounded by the press-welded line portion H1.Besides, the press-welded line portions H1, H2, H3 and the press-weldeddot portions Hd are formed where they do not overlap with each other.That is, as shown in FIG. 2, the space between the press-welded lineportion H1 and the press-welded dot portions Hd which are situatedinside the portion surrounded by H1 and the space between thepress-welded line portion H1 and the press-welded dot portion Hd locatedoutside the portion (i) surrounded by H1 are approximately the same (δ,for example, between 1 mm and 5 mm) or more than δ. Likewise, withrespect to the press-welded dot portions Hd between the press-weldedline portions H1 and H2, the space between the press-welded dot portionsHd and press-welded line portion H1 and the space between thepress-welded dot portions Hd and press-welded line portion H2 are equalto, or more than the space δ.

[0057] In addition, the outer periphery of the pattern “chick” expressedby the press-welded line portion H1 is surrounded in an approximatelysquare shape by the press-welded line portions H4 which areapproximately linear. This press-welded line portions H4 and thepress-welded dot portions Hd do not overlap with each other. The spacebetween the press-welded line portions H4 and press-welded dot portionsHd is equal to, or more than, the space 6.

[0058] The press-welded line portions H5 are also formed which surroundthe “chick” together with the press-welded line portions H4. Thepress-welded line portion H5 expresses a “flower”, and is mainly made ofa curved line. The press-welded line portion H5 forms the surroundedportion (ii). Since the area of the surrounded portion (ii) is small,the press-welded dot portions Hd are not formed inside the surroundedportion (ii). This press-welded line portions H5 are formed such thatthey do not overlap with the press-welded dot portions Hd. The spacebetween the contour of the press-welded line portions H5 and thepress-welded dot portion Hd is also equal to, or more than, the space δ.

[0059] Thus, in the nonwoven fabric S, the figures “chick”, “surroundingline”, “flower” and the like are expressed by the press-welded lineportions H1, H2, H3, H4, H5, and the press-welded dot portions Hd areformed in the portions other than the press-welded line portions H1, H2,H3, H4, H5. The press-welded portions are surely spaced apart at thefixed space δ or at a space more than δ, whereby the portions in whichthermoplastic fibers are not welded occupy at least a fixed area in thepatterns A to P. Further, the press-welded dot portions Hd aredistributed such that the volume ratio of the press-welded portions tothe portions other than the press-welded portions is approximately fixedthroughout the nonwoven fabric S.

[0060] In the patterns A, B, . . . in FIG. 1, the figures “star”,“leaf”, “sun”, “cloud” and the like are drawn instead of the figure“chick”. The relation between the press-welded line portions by which todraw these figures and the press-welded dot portions is the same as thatin the pattern E shown in FIG. 2.

[0061]FIG. 3 is an enlarged view of a part of the press-welded lineportions H1, H2, H5 shown in FIG. 2. In the press-welded line portionsH1, H2, . . . , Hd, the fibrous web W formed of thermoplastic fibers ispartially pressed and welded, and the thickness of the welded portionsis smaller than that of the non-welded portion. In the press-weldedportions, the nonwoven fabric is recessed in one surface. The thicknessof the nonwoven fabric S in the press-welded portion is approximately0.1 mm, and the specific volume thereof is at least approximately 3cm³/g and at most 10 cm³/g, for example, 4.3 cm³/g. The thickness of thenon-press-welded portions in the nonwoven fabric S is 0.5 mm, and thespecific volume is at least approximately 10 cm³/g and at most 30 cm³/g,for example, 21.7 cm³/g.

[0062] The difference in the thickness between the press-welded portionsand the non-press-welded portions of the nonwoven fabric S results inraising the surface of the fibrous web W (nonwoven fabric S) in theboundary therebetween. When the press-welded line portions (H1 and thelike) are provided, the boundary line between the press-welded portionsand the non-press-welded portions continuously extends long, and theraised portion on the surface of the fibrous web W (nonwoven fabric S)indicated at (iv) in FIG. 3 is continuously formed long. Accordingly,the portion (iv) looks raised in comparison to the surroundingpress-welded dot portions Hd. Therefore, when the press-welded lineportion is long, the overall nonwoven fabric looks raised and feelsbulky when one touches it with the hand. For example, in FIG. 2, thepress-welded line portion H1 which is a contour of the figure “chick” islong and surrounds the portion (i). Accordingly, in this surroundedportion (i), the shape “chick” looks raised from the overall surface ofthe nonwoven fabric S. Further, the surrounded portion (ii) having asmall area is formed from the press-welded line portions H5 having thefigure “flower”. Since the press-welded line portion is not formed inthis surrounded portions (ii), the fibrous web W (nonwoven fabric S) ofthis surrounded portions (ii) looks raised.

[0063] When the press-welded line portions H1, H2, H3, . . . extend longwith a predetermined width, the raised portion on the surface of thefibrous web W becomes conspicuous in the boundary of the press-weldedline portions, and looks bulky and soft as a whole.

[0064] In the press-welded line portions H1, H2, . . . and Hd, thethermoplastic fibers are pressed and hot-melted; these fibers are weldedand become filmy. These press-welded line portions are transparent orsemitransparent. Since the fibrous web has a high bulkiness in thenon-press-welded portions, these portions have a white orsemitransparent white color. The press-welded dot portions Hd are alsofilmy. However, since each of the press-welded dot portions Hd has asmall area, the color contrast with the surroundings is not so clear. Onthe other hand, the press-welded line portions H1, H2, H3, H4, H5 arelinear, and the transparent or semitransparent filmy portions extendlong with a predetermined width. Consequently, the filmy press-weldedline portions are conspicuous, and the color contrast between thepress-welded line portions H1, H2, H3, H4, H5 and the other portionsbecomes clear. Since the contrast therebetween becomes clear, the figure“chick” provided by the press-welded line portion H1, the square of thepress-welded line portions H4 that surrounds this figure and the figure“flower” provided by the press-welded line portions H5 look clear.

[0065] When a fiber having a star-like, triangular or squarecross-sectional shape shown in (A), (B) or (C) of FIG. 4 is used as thestarting fiber of the fibrous web, the difference between thepress-welded line portions H1, H2, . . . and the non-press-weldedportions can be made even clearer. When light is applied to the fiberhaving the cross-sectional shape shown in (A), (B) or (C) of FIG. 4, thelight is reflected diffusely on the surface of this fiber, and thefibrous web W formed of this fiber comes to have a clear white color.Consequently, the non-press-welded raised portions of the nonwovenfabric S come to have a clear white color, and are sharply contrastedwith the transparent or semitransparent filmy press-welded line portionsH1, H2, . . . . As a result, the figures formed by the press-weldedportions H1, H2, . . . become conspicuous.

[0066] The press-welded line portions H1, H2, . . . and the press-weldeddot portions Hd are arranged such that these two types of the portionsdo not overlap with each other, and they are spaced apart from eachother at a predetermined space of □ or more. Consequently, it does nothappen that the patterns expressed with the press-welded line portionsH1, H2, . . . are hidden by the press-welded dot portions Hd. Since thepress-welded dot portions Hd are formed at a fixed space where thepress-welded line portions H1, H2, . . . are not formed, thethermoplastic fibers can surely be kept not to come out from the overallnonwoven fabric S, making it possible to prevent the fluffing of thefibrous web W (nonwoven fabric S).

[0067] In order to make the figures drawn by the press-welded lineportions H1, H2, H3, . . . much clearer than the press-welded dotportions Hd, it is advisable that the areas of the press-welded lineportions H1, H2, H3, that give the figures are the same as, or largerthan, the areas of the press-welded dot portions Hd. The total area ofthe press-welded line portions H1, H2, H3, . . . and Hd is preferably atleast 10% and at most 35%, more preferably at least 15% and at most 25%based on the area of the surface of the nonwoven fabric S. The formationof the press-welded portions at such an area ratio helps to secure thestrength of the nonwoven fabric S, to prevent fluffing of the fibrousweb (nonwoven fabric S), to make the figures approximately clear and tomaintain the air permeability of the nonwoven fabric S.

[0068] For the figures drawn by the press-welded line portions H1, H2,H3 . . . to be made even clearer, it is advisable to overlay a colorresin sheet on the reverse surface of the nonwoven fabric S and adherethem after the production of the nonwoven fabric S having thepress-welded line portions. FIG. 5 illustrates a state where a colorsheet T is put under the nonwoven fabric S. Since the press-welded lineportions H1, H2, H3 . . . are transparent or semitransparent, the colorof the color sheet is seen through the reverse surface of the nonwovenfabric S in the press-welded line portions H1, H2, H3, . . . , and thepress-welded line portions H1, H2, H3, . . . look colored. Meanwhile,the portions other than the press-welded line portions are white becauseof the high bulkiness of the fibrous web W (nonwoven fabric S), and thecolor of the color sheet T is hardly seen therethrough. As a result, thecontrast between the press-welded line portions H1, H2, H3, . . .through which the color of the color sheet T is seen and the whiteportions other than the press-welded line portions is much sharper, andthe figures are rendered clearer.

[0069] In this case, various color sheets are available as the colorsheet T. The color sheet T may be a colored resin film or a nonwovenfabric S formed of dyed or colored fibers. For example, when a colorsheet T having a warm color such as light pink is used, a softimpression can be given to a user owing to the color which is seenthrough the press-welded portions. When using a blue color, a clean orfresh impression can be given.

[0070] In a method of adhering the color sheet T to the reverse surfaceof the nonwoven fabric S, a hot melt adhesive is spirally coated on thereverse surface of the nonwoven fabric S or/and the surface of the colorsheet T, and the nonwoven fabric S and the color sheet T are adhered toeach other either partially or wholly.

[0071] A color film having a thermoplastic sheet laminated thereon isalso available as the color sheet T. When a nonwoven fabric containingthermoplastic fibers such as polyethylene fibers or polypropylene fibersis used as the color sheet, it is possible to weld the color sheettogether with the fibrous web W at the same time when the press-weldedline portions H1, H2, . . . are formed in the fibrous web W as will belater described.

[0072]FIG. 6 illustrates a disposable diaper 1 for babies or littlechildren as an example using the nonwoven fabric S.

[0073] The diaper 1 shown in FIG. 6 is called an “open-type diaper”. Thereverse portion 3 thereof is put on the bottom of babies. The frontportion 2 is attached to the stomach of babies by being held between thelegs. Overlap portions 4 of the reverse and front portions 3, 2 areadhered using an adhesive tape or a fastener.

[0074] In this diaper 1, a top sheet (inner sheet) 5 such as a nonwovenfabric or the like is disposed on the inner surface in contact with theuser's skin, an absorbent is put on the outer surface thereof, and aback sheet (outer sheet) 6 is placed on the outer surface of theabsorbent. In a diaper shown in FIG. 6, the nonwoven fabric S shown inFIG. 1 is overlaid as the back sheet 6 on the outer surface of anair-permeable and liquid-impermeable resin film (outer film).

[0075] Since the nonwoven fabric S which looks soft and feels soft isdisposed on the outermost surface of this disposable diaper 1, one feelscomfortable and has a touch close to that of underwear. Besides, as thefigures such as “chick”, “star”, “flower” and the like are drawn on theoutermost surface, this diaper has an appropriate appearance as aproduct for babies. Since the outer film and the nonwoven fabric S areadhered to each other using an adhesive, the air permeability of theresin film is not inhibited. Further, when using a product in which thecolor sheet T is adhered to the reverse surface of the nonwoven fabric Sas shown in FIG. 5, the color of the color sheet T on the reversesurface is seen through the press-welded portions of the nonwoven fabricS, and the figure can easily be seen, providing an excellent appearance.When the color of the color sheet T is changed depending on sizes ofdiapers, the diapers of various sizes can be grouped according to thecolors. In this case as well, the outer film and the color sheet T areadhered using an adhesive, so that the air permeability of the resinfilm is not inhibited.

[0076] In the press-welded line portions H1, H2, H3, . . . expressingthe figures, the nonwoven fabric S is filmy and transparent orsemitransparent. Accordingly, when the amount of urine absorbed into thediaper is increased, the color of urine is seen through the press-weldedline portions H1, H2, H3, . . . , making it possible to observe thepresence or absence of urine from outside the diaper. Especially whenfibers having the cross-sectional shape shown in FIG. 4 are used as astarting material of the nonwoven fabric, the raised portions other thanthe press-welded line portions H1, H2, H3, . . . of the nonwoven fabricS become whiter, and give a sharper contract with the press-welded lineportions H1, H2, H3, . . . which are filmy and transparent orsemitransparent. Thus, the color of urine can easily be observed fromoutside the diaper.

[0077] The process for producing the nonwoven fabric S is describedbelow.

[0078] This nonwoven fabric S can be produced by changing the shape ofthe projected portions of the hot roller in a conventional process forproducing a nonwoven fabric.

[0079] First, thermoplastic short fibers which are fluffed by stretchingand cutting a resin are sucked, and formed into a sheet on a conveyor togive a fibrous web W having a base weight of, for example, at leastapproximately 15 g/m² and at most 40 g/m².

[0080] This fibrous web W is partially welded using hot rollers. Aroller 11 provided on the surface with projected portions 11 a and aroller 12 having a smooth surface as shown in FIG. 7 are used as the hotrollers. A sheet (fibrous web W) formed of thermoplastic fibers is fedbetween the rollers 11 and 12 as shown in FIG. 8. At this time, thefibrous web W is partially pressed from one surface by means of theprojected portions 11 a of the hot roller 11 to hot-weld thethermoplastic resins of the fibrous web W. The press-welded lineportions H1, H2, H3, . . . which are recessed in one surface of thefibrous web W and the press-welded dot portions Hd are thus formed. Whenthe projected portions 11 a on the surface of the hot roller 11 have thepattern shown in FIG. 1 or 2, the press-welded line portions H1, H2, H3,. . . and the press-welded dot portions Hd are formed in the resultingnonwoven fabric S.

[0081] When the color sheet T is adhered to the reverse surface of thenonwoven fabric S, a color resin film or a color nonwoven fabriccontaining thermoplastic fibers is laminated on the reverse surface ofthe fibrous web W, and the laminate is fed between the hot rollers 11and 12 shown in FIGS. 7 and 8. When the press-welded line portions H1,H2, H3, . . . are formed in the fibrous web W by the projected portions11 a of the hot roller 11, the color resin film or the color nonwovenfabric and the fibrous web W are press-welded with each other in thepress-welded line portions H1, H2, H3 . . . . As a result, the nonwovenfabric S and the color sheet T can easily be adhered to each other, andthe color can appear in the press-welded line portions.

[0082] The fibrous web W shown in FIG. 8 has two layers, namely a layerformed of dyed or colored fibers as an under layer, and an uncoloredfibrous layer formed of fibers having the cross-sectional shape shownin, for example, FIG. 4(A), (B) or (C) as an upper layer. It is alsopossible that the two-layered fibrous web W is fed between the hotrollers 11 and 12 and the press-welded line portions H1, H2, H3, . . .are formed through the projected portions 11 a. Then, the portionsobtained by welding the fibers contained in the two layers become thepress-welded portions. Since the press-welded portions come to be filmy,the color appears in the press-welded portions, and the sharp colorcontrast is given between the press-welded portions and thenon-press-welded portions.

[0083] In the present invention, the press-welded line portions having acurved shape or a square shape are not necessarily continuous lines. Forexample, in FIG. 2, the press-welded line portion H1 drawing the contourof the “chick” may be an uncontinuous line(broken line), not acontinuous line. The uncontinuous line refers to a line which is brokeneither partially or continuously.

[0084] As stated above, in the nonwoven fabric which is partiallypressed and in which the thermoplastic fibers of the pressed portionsare welded, the press-welded portions are formed into continuous line oruncontinuous line portions and dot portions, making it possible toobtain a highly bulky nonwoven fabric and give a soft impression to auser.

[0085] Further, the nonwoven fabric can have an excellent appearanceunexpected from the conventional nonwoven fabric by drawing the patternwith the continuous line or uncontinuous line press-welded lineportions.

[0086] Especially when the nonwoven fabric is formed of starting fibershaving the square or uneven cross-sectional shape or the color resinsheet is overlaid under the nonwoven fabric, the figure drawn in thenonwoven fabric can be made much clearer.

What is claimed is:
 1. A nonwoven fabric characterized in that a fibrousweb formed of thermoplastic fibers or containing thermoplastic fibers ispartially pressed and heated to form recessed press-welded portions, thefibers in the portions other than said recessed portions being raised;said press-welded portions are continuous lines or uncontinuous lineswhich give a pattern of figures, characters or signals containing atleast curved portions or square portions, or a pattern of a combinationthereof; and a plurality of press-welded dot portions are formed in theportions other than the continuous line or uncontinuous linepress-welded portions such that said press-welded dot portions do notoverlap with the continuous line or uncontinuous line press-weldedportions.
 2. The nonwoven fabric according to claim 1 , wherein the baseweight of the fibrous web is at least 15 g/m² and at most 45 g/m², thespecific volume of the press-welded portions formed in the fibrous webis at least 3 cm³/g and at most 10 cm³/g, and the specific volume of thenon-press-welded portions is at least 10 cm³/g and at most 30 cm³/g. 3.The nonwoven fabric according to claim 1 , wherein a portion surroundedby the continuous line or the uncontinuous line press-welded portion isformed, and the fibers are raised in this surrounded portion.
 4. Thenonwoven fabric according to claim 1 , wherein the total area of thepress-welded dot portions is the same as, or less than, the total areaof the continuous line or uncontinuous line press-welded portions. 5.The nonwoven fabric according to claim 1 , wherein the continuous lineor uncontinuous line press-welded portions are spaced apart from thepress-welded dot portions at a space of at least 1 mm and at most 5 mm.6. The nonwoven fabric according to claim 1 , wherein the startingfibers of the fibrous web have a square cross-sectional shape.
 7. Thenonwoven fabric according to claim 1 , wherein the fibers are melted inthe press-welded portions, and said portions become filmy.
 8. Thenonwoven fabric according to claim 7 , wherein a color sheet islaminated on the reverse surface of the nonwoven fabric, and the colorof the color sheet laminated on the reverse surface is seen through thepress-welded portions of the nonwoven fabric.
 9. A process for producinga nonwoven fabric comprising the following steps: a step of forming afibrous web with thermoplastic fibers or fibers containing thermoplasticfibers, a step of feeding said fibrous web between a hot roller providedon the surface with projected portions containing continuous lines oruncontinuous lines by which to form figures, characters or symbolshaving at least curved portions or square portions, or a combinationthereof, and a hot roller having a smooth surface, and a step of holdingthe fibrous web between the hot roller provided on the surface with theprojected portions and the hot roller having the smooth surface, andpress-welding the fibers of the fibrous web with the projected portionsto partially recess the fibrous web and form press-welded portions. 10.The process of producing a nonwoven fabric according to claim 9 ,wherein a plurality of projected dot portions are formed on the hotroller besides the continuous line or uncontinuous line projectedportions.
 11. The process of producing a nonwoven fabric according toclaim 9 , wherein a colorless fibrous web is laminated on a dyed orcolored thermoplastic sheet, the laminate is held between both of thehot rollers, and the thermoplastic sheet and the fibrous web of thelaminate are together press-welded with the projected portions of thehot roller to form press-welded portions.
 12. The process according toclaim 9 , wherein a fibrous web formed of colorless fibers is laminatedon a fibrous web formed of dyed or colored fibers, the thus-laminatedfibrous webs are held between both of the hot rollers, and the coloredfibrous web and the colorless fibrous web are partially press-weldedtogether with the projected portions of the hot roller to formpress-welded portions.